Perhaps more important than perfect physical fitness to the would-be conqueror of Everest is the possession of the correct mentality. Absolutely essential are singleness of aim, namely, the attainment of the summit, and unswerving faith in the possibility of its achievement. Half-heartedness in even one member of the attacking party spells almost certain failure. Many a strong party in the Alps has failed to reach its objective through the depressing effect of the presence of one doubting Thomas. Like an insidious disease, a wavering, infirm belief is liable to spread and cause the destruction of the hopes of those who come into contact with it. The man who cannot face Mount Everest without at the same time proclaiming that the mountain has the odds in its favour would do better by himself and others to leave the proposition severely alone. Of almost equal importance is the possession of what may be called mental energy or will power, or simply “go.” Mountaineers may be divided into two classes according to their behaviour when, tired and well-nigh exhausted, they are called upon to make yet one more supreme effort. There are those who, lacking the will power necessary to force their jaded bodies on to still further action, give in; others, possessed of an almost inexhaustible fund of mental energy, will rise to the occasion, not once, but time and again. Physical pain is the safety valve which nature has provided to prevent harm being done to the body by exhaustion. But nature’s margin of safety is a wide one. On Everest, this margin must be narrowed down, if necessary, to vanishing-point; and this can only be done by the climber whose fund of mental energy is sufficient to drive his body on and on, no matter how intense the pains of exhaustion, even to destruction if need be. ------------------------------------------------------------------------ CHAPTER IX NOTES ON EQUIPMENT Our recent experiences having shown that the greatest altitude at which acclimatisation takes place is about 22,000 feet above sea-level, it may be reasonably assumed that, from the climber’s point of view, high altitude on Mount Everest begins at that height. Incidentally, also, on approaching the North Col over the East Rongbuk Glacier, the snow and ice conditions met with up to this level approximate very closely to summer conditions in the Alps. Above 22,000 feet, however, such conditions, particularly the state of the snow, resemble those met with in the Alps in mid-winter. This high-altitude zone may be further divided into two sub-zones—the first, from 22,000 feet (the foot of the steep snow and ice slopes leading up to the North Col) to 23,000 feet, in which climatic conditions are by no means severe, as the North Col affords protection from the prevailing west wind; and the second, from 23,000 feet onwards, of which extreme cold and strong wind are the predominant characteristics.